1. Field of the Invention
The present invention relates to a technology of voltage detection utilizing an electro-optic (E-O) material, and particularly to a E-O probe employing an electro-optic material and a fiber optic plate (FOP), and a two-dimensional voltage detecting apparatus using the E-O probe.
2. Related Background Art
In the conventional art, there is known a non-contacting type of two-dimensional voltage distribution detector utilizing an electro-optic modulator. FIG. 14 illustrates an example of the configuration of such an apparatus. This apparatus has an optical system which is arranged in the following manner. Through a lens 130, light from a light source 140 two-dimensionally irradiates an E-O probe 120 placed in the proximity of electrodes 212 on an object to be measured (for example, IC, liquid crystal panel etc.) 210, and reflected light from the E-O probe 120 is taken by a camera 160. A total reflection mirror 124 is formed on a surface of the E-O probe 120 facing the object to be measured 210, and a transparent electrode (ITO) 123 is formed on the other surface and is electrically connected to ground. Interposed therebetween is an electro-optic material 122. The refractive index of the electro-optic material 122 is varied in accordance with the electric field E generated between the electrodes 212 and the transparent electrode (ITO) 123. Furthermore, the refractive index is different at each portion of the electro-optic material 122 in accordance with the strength of the electric field E in that portion.
The circular polarization state of the light from the light source 140 is the same before the light enters the E-O probe 120, but the polarization state of the light reflected by the E-O probe 120 is different because of the difference of the refractive index from portion to portion in the electro-optic material 122. The different polarization states are converted into difficult intensities after the light passes through an analyzer 150. The light is then detected by a camera 160 as a two dimensional image. This image is processed by a computer, such that the voltage applied to the electrodes 212 on the measured object 210 can be displayed on a computer screen 176 and observed as a two dimensional image.
FIG. 15 also shows an example of the configuration of a two-dimensional voltage distribution detector using an electro-optic modulator. In the optical system of this apparatus, a light source 140 for emitting collimated light is used. The collimated light irradiates an E-O probe 120 by a polarizing beam splitter 152, and the intensity of the light reflected by the E-O probe 120 is two-dimensionally detected by a camera 160. Also with this configuration, after the signal from the camera 160 is processed by an imager 172 and an image processor 174, the voltage applied to the measured electrodes 212 on the object 210 is displayed on the computer screen 176, so that a two-dimensional voltage image can be observed.
These apparatus as can be used, for example, to inspect wiring defects and the like in a liquid crystal panel by applying voltage thereto during the manufacturing process after formation of TFTs (thin film transistors) and wiring has been completed. The conventional E-O probe 120 has a configuration shown in FIG. 16 in which an electro-optic material 122 and a reflecting mirror 124 are formed on a glass substrate 125. Another proposed E-O probe is shown in FIG. 17, in which a plurality of elongated electro-optic materials 122 are placed and separated by the electrodes 126. The electrodes 126 are used to generate the electric field E in conjuction with the electrode 212. This configuration makes the two dimensional detection of the voltage distribution easier.
In the two-dimensional voltage distribution detectors as shown in FIGS. 14 and 15, the spatial resolution is inferior and the discrimination between adjacent electrodes is difficult. Particularly, these detectors cannot effectively evaluate ICs where space between electrodes is narrow due to high integration. Moreover, it is difficult to make a large modulator and even if the large modulator was made, the large area could not be measured at once because the optical system of the detector is complicated.
Therefore, there is a great need in the art for; a two-dimensional voltage detecting apparatus having high spatial resolution.